The purpose of this proposal is to understand the relationship between membrane architecture and function in photosynthetic membranes. Our approach will be via discrete, yet correlative, techniques using the unicellular, transformable cyanobacteria, Anacystis nidulans. Our strategy will consist of five major experimental techniques: (1) the isolation of temperature-sensitive mutants that are defective in photosynthesis; (2) characterization of the structural and functional defect of each mutant using biophysical and biochemical procedures; (3) isolation of sub-membrane aggregates that are enriched in either Photosystem I and II or that contain the chlorophyll-protein complexes; (4) labelling of proteins with permeant and impermeant probes to determine the localization of proteins with respect to the lipid bilayer; and (5) cloning of photosynthetic genes and the synthesis of the gene produce coded by the specific genes. The specific information that should be obtained by this proposal include: (1) the effects of mutation on membrane structure and function; (2) the protein composition of the membrane as well as that of membrane aggregates such as reaction centers and chlorophyll protein complexes; (3) the precise location of these components in the membrane, including thier arrangement as internal or external proteins and their nearest neighbors; (4) how variations in membrane structure lead to functional aberrations and alter the distribution of energy between the photosystems; (5) the cloning of genes coding for photosynthetic functions; the gene product of the cloned gene can then be synthesized, thus yielding a precise correlation between structure and function; (6) a genetic map of the photosynthetic genes in A. nidulans; and (7) construction of a hybrid plasmid that can replicate in both A. nidulans and E. coli. This will enable cloning of genes directly in cyanobacteria, but allow the recombinant plasmid to be grown in bacteria for further analysis.